Investigation of trunk muscle endurance and standing balance according to severity of disability in women with moderate to severe disability due to neck pain.

Objectives: To investigate the association between trunk muscle endurance, standing balance, and neck disability in women with chronic neck pain (CNP) and to compare trunk muscle endurance and standing balance according to disability severity.

Methods: Thirty-one women with CNP and Neck Disability Index scores of 30%-70% were included. Isometric endurance times of neck flexors, trunk flexors, extensors, and lateral flexors were measured. Overall stability index (OSI), anterior/posterior stability index (APSI), and medial/lateral stability index (MLSI) were obtained to assess standing balance under the following conditions: eyes-open on a firm surface (EO-Firm), eyes-closed on a firm surface, eyes-open on foam, and eyes-closed on foam (EC-Foam). Higher index scores indicate larger postural sway. Linear regression analysis was used for association. Participants were divided into two groups based on their disability scores, either having moderate or severe disability, and the groups were compared.

Results: Trunk flexor endurance time had an effect on disability (R-squared=0.18, F(1.29)=6.453) and APSI under the EC-Foam condition (R-squared=0.17, F(1.29)=6.105) (p<0.05). Trunk extensor endurance time had an effect on OSI under the EO-Firm condition (R-squared=0.14, F(1.29)=4.775, p<0.05). Women with moderate disability had longer endurance times than those with severe disability for trunk flexors (Cohen's d=0.89, p<0.05).

Conclusion: Isometric endurance times of trunk flexors and extensors were associated with standing balance in women with CNP. Trunk flexor endurance was also associated with neck disability. Furthermore, women with moderate disability had better trunk flexor endurance than those with severe disability, with a large effect size.